Electric switch and means to delay the successive opening thereof



July 18, 1933. AINSWQRTH 1,918,368

ELECTRIC SWITCH AND IEANS TO DELAY THE SUCCESSIVE OPENING THEREOF FiledMay 31, 1929 Irzven 202.

mi) MM Patented July 18, 1933 UNITED STATES PATENT OFFICE CHESTER D.AINSWOBTH, OF WOLLASTON, MASSACHUSETTS, ASSIGNOB TO CONDIT ELECTRICALMANUFACTURING CORPORATION, OF SOUTH BOSTON, MASSACHUSETTS,

A CORPORATION OF MASSACHUSETTS ELECTRIC SWITCHAND MEANS T DELAY THESUCCESSIVE OPENING THEREOF Application filed May 31,

This invention relates to electro1nagnetically controlled electricswitches and to closing and opening apparatus and clrcults therefor. V

It frequently happens that an operative, especially with switchesadapted for the control of industrial apparatus, as motors, re peatedlyopens and close the switch rapidly when there is no need for it, therebyunnecessarily heating the contact members of the switch and drawingdestructive arcs between them and also placing unusual demands upon thecircuit of the switch and the apparatus associated therewith.

It is an object of the present invention to provide an electricswitch'and its control apparatus and circuits with means so arrangedthat after the switchhas once been opened, it

can not again be reclosed untilthe expiration of a predetermined timeinterval, which interval is adapted to be suflicientlylong to permit thecontact members to become cool and the hot arc gases to be dissipated.

The switch with which'the present invention'particularly is concerned isan electro magnetically operated switch having an electro-magnet that isadapted to be energized to close the switch and to be maintainedenergized for so long as the switch is to be held closed. The controlapparatus for such a switch includesa push button operated circuitcontroller to insure the initial energization of the electro magnet andthe closing of the switchand a second push button operated circuitcontroller that is adapted to be operated to break the circuit of theelectro-magnet V and permit the switch to open. The first or V isnormally closed.

1929. Serial No. 367,433.

switch for a predetermined time interval after it has been opened underload.

A further object of the invention is generally to improve theconstruction and opera tionof electric switches and control apparatusand systems therefor.

Fig 1 is adiagrammatic illustration of the switch and its controlapparatus and circuits embodying the present invention. 7

Fig. 2 is similar to Fig. 1 except that a modified arrangement isprovided for preventing rapid reclosing operations of the switch. f

Fig. 3 is a modification of Fig. 1 wherein a normally open thermal relayis substituted for the electro-magnetic relay.

The switch with which the present invention is particularly concernedincludes a movable bridging member which is adapted to be moved upwardlyto engage and bridge the stationary contact members 12 which areincluded in series with one of the circuit conductors 14 of the hereinshown single phase circuit that includes the other conductor 16. Theswitch may control the supply of power to any power consuming device asthe motor 18. While the switch here-shown is illustrated as being in butone conductor of the circuit, it is to be understood that the switch canhave cooperating contact members ar ranged in all. of the conductors ofthe circuit as is common practice. The bridging member 10 is mounted onan insulating bar 20 carried by the switch arm 22 which is pivotedloosely at its free end to one leg of an electro-magnet 24 which has anactuating winding 26. The arrangementis such that when said winding isenergized, the electr c-magnet attracts the lever 22 and moves thebridging member into engagement with the fixed contact member 12.thereby closing the switch. The switch is held closed by maintaining theelectro-magnet energized. The circuit of the electro-magnet iscontrolled by a pair of pushbutton con trolled circuit controllers,there being the starting push button 28 which is arranged to initiallyenergize the magnet to efl'ect the closing of the switch and a second orstopping push button 30 which serves to efi'ect the de' 1,a1a,m' Oi i atthe opening f" thermal element comprises a metal'strip that j is of twqmmhgving we f xpansim' secured flu m mmfillwfi amiomaw'mm 58 which areinfilmidgin the c'bndue- P tty aw firm 2 18pontrols inring Elation withsaid elemen fi. Said im gpeeificaillyto I In the modificationillustrated in Fig.2, the electro-magnetic relay 60 is replaced by anormally-closed thermal relay 70 which is vhereshown as identical withthe construction troller and the electro-magnet winding.

With this arrangement, the heating element 72 is normally (lo-energizedexcept for the time that the starting circuit controller is closed. .Therelay is so designed that the contact members 74: are'not adapted toseparateby the momentary current traversing the conductor 50. theadjustment being such thatthe contacts74 will not open if the startingcircuit controller is but momentarily closed, which is all. that isnecessary to effect the closing of the switch.

If, however, it is attempted to reclose the SWltCh repeatedly andrapidly by successive operations of the starting push button, theaccumulation of heat in the thermal member is adapted to be such thatafter two or three rapidly repeated operations, the thermal memberexpands and separates the contact members 74. thereby disabling theholding circuit 48 and preventing further reclosures of the switch untilthe thermal relay has dissipated its heat. Usually a switch can beopened rapidly a few times under its rated load without undue arcing butif the opening I operations are continued, the accumulation of heat andarc gases thereafter results in destructive arcing. Thus,.thearrangement shown in Fig. 2 will prevent rapidly repeated openings ofthe switch under load.

The broader idea of preventing the switch from being repeatedly openedrapidly'under load is described and claimed in a copending applicationof George A. Burnham, Serial No. 367,340, filed May 31, 1929, andassigned to the assignee of this present application.

In Fig. 3, the arrangement is the same as 'in Fig.1 except that anormally-open thermoresponsive relay 80 is substituted for theelectro-magnetic relay 60. The electric resistance heating element 82 ofsaid thermal relay is included in series with the closing circuit 48 andthus is maintained heated for so long as the switch is closed. Thethermoresponsive element 84 is maintained in flexed condition by theheated element 82 and thereby maintains the contact members 86 inseparated condition. When the switch is opened, however, either onoverload, or by depressing the stopping button 30, the current flow 1nthe closing circuit 48 is interrupted and the thermo-responsive elementcools OE and ulti- Inately closes the contacts 86. Until these contactsare closed, however, no effect results from the operation of thestarting push button 28 and the period of time required for the contacts80 to close is adapted to be sufiicient to provide the desired timedelay between successive opening and closing operations of the switch.

, I claim:

1. The combination of an electric switch, electromagnetic means forcontrolling the closing and opening of the switch, closing and openingcircuits for said electromagnetic means, closing and opening circuitcontrollers'associated with said respective circuits, and electricalmeans also associated with both and energized from one of said circuitsarranged to disable the other circuit :for a period of time sufficientto prevent the rapidly and indefinitely repeated opening of the switch.

2. The combination of an electric switch, electro-magnetic means forcontrolling the closing and opening of the switch, closing and openingcircuits for said electro-magnetic means, closing and opening circuitcontrollers associated with said respective circuits, and electricalmeans operated by the current in one circuit to disable the othercircuit for a period of time suflicient to prevent the rapidly repeatedopening of the switch under load. V

3. The combination of an electric switch, electro-magnetic means forcontrolling the closing and opening of the switch, closing and openingcircuits for said electro-magnetic means, closing and opening circuitcontrollers associated with said respective circuits, separable contactmembers included in one of said circuits, and means actuated by thecurrent in said other circuit to effect the control of said contactmembers and delay the successiveopenings of the switch.

4. The combination of an electric switch, electro-magnetic means forgoverning the closing and opening of the switch, closing and openingcircuits for said electro-magnetic means, closing and opening circuitcontrollers associated with said respective circuits, separable contactmembers in one of said circuits, and time-delayed means actuated by thecurrent in said other circuit to control said contact members and delaythe reclosing of the switch after an opening thereof.

5. The combination of an electric switch, electro-magnetic means forgoverning the closing and opening of the switch, closing and openingcircuits for said electro-magnetic means, closing and opening circuitcontrollers associated with said respective circuits, andthermally-actuated means controlled by the current in one of saidcircuits and having control of said other circuit to delay the reclosingof the switch following its opening.

